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Watersheds

Watersheds. Outcomes. Read a contour map Delineate a watershed Determine slopes/lengths Determine a drainage area. We All Live in a Watershed. When water runs off your property where does it go?. Importance of Watersheds. Pollutants can enter waterbodies

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Watersheds

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  1. Watersheds

  2. Outcomes • Read a contour map • Delineate a watershed • Determine slopes/lengths • Determine a drainage area

  3. We All Live in a Watershed When water runs off your property where does it go?

  4. Importance of Watersheds • Pollutants can enter waterbodies • Silt from construction sites, farms, erosion • Septic system waste • Fertilizers, pesticides • Road salt • Other pollutants (industry/commercial)

  5. Watershed Protection • SPDES (stormwater pollution discharge and elimination system) • Watershed action plans • Public Involvement (stewardship)

  6. Watershed • Any particular point on a water channel (stream, ditch, gutter, etc.) has an associated watershed area • The boundaries of a watershed are ridge lines (high points) • You can identify ridge lines by contour lines on topographic maps

  7. Contour Maps-Lines showing constant elevation

  8. Hints for reading contour maps • Flow paths are perpendicular to contour lines (why?) • Streams---Contour lines are concave (think V’s) • Ridges----Contour lines are convex (think noses) • Peaks of mountains and depressions (swamps, ponds) usually show as small circular areas • Contour lines close together indicate steep slopes • Contour lines which are far apart indicate flat slopes • Highlight rivers/creeks to your point of interest (it also sometimes helps to highlight them outside your point of interest) • Ignore roads; ideally, any construction project shouldn’t shift water to another watershed

  9. Steps-Delineating Drainage Areas • Identify your point of interest • Identify the channels/subchannels (V’s) • Identify the hill tops (circles) • Draw from hill-top to hill-top along the ridges (noses)

  10. Delineate Watershed • Class Exercise (Handout Figure II-1) • Spend 5 minutes delineating watershed

  11. Sub-Drainage Areas • Drainage areas may be broken up into sub-catchments or sub-drainage areas because: • Drainage areas are usually modeled as homogeneous systems • Streams are branched • Points of interest need to be isolated

  12. Delineate Subareas Class exercise Spend 5 minutes delineating subareas for each reach Handout answers (Figure II-2 and II-3)

  13. Break

  14. Determining Drainage Areas • Stripping Method • Grid Method • Planimeter • Software Programs (GIS)

  15. Stripping/Grid Methods http://www.globalsecurity.org/military/library/policy/army/fm/5-430-00-1/fig6-13.gif

  16. Planimeter

  17. Software http://gis.esri.com/library/userconf/proc99/proceed/papers/pap676/p6764.gif

  18. Determining Lengths Edge of Paper Tic Method String Method (non-stretch string) Don’t use “as the crow flies” Check scale (1”=2000’ or other) 20

  19. Data Collection • Land Use • Soil Characteristics • Slope (overland and channel) • Channel/Overland flow lengths • % Impervious • Channel cross-sections • Roughness characteristics • Storage (ponds, swamps, wetlands)

  20. Sources • Field reconnaisance • Aerial Photographs • NRCS Soil Maps • USGS Maps/Other Contour Maps • Planimetric mapping • Historical engineering studies • Survey Data • Soil Boring Data

  21. Common Conversions • 1 acre = 43,560 ft2 • 1mi2 = 640 acres • 1 hectare = (100 m)2 = 10,000 m2 • 1 acre = 0.405 hectare • 1 hectare = 2.46 acres • 1 meter = 3.2808 feet • 1 foot = 0.3045 meter

  22. Downloading USGS Maps *.pdf http://store.usgs.gov/b2c_usgs/b2c/start.do

  23. Other tools: • Image capture software: • Snipping Tool (on engineering computers) • In adobe reader use tools, select and zoom, snapshot tool, to capture images • USGS pdf’s---click on images, click off orthoimages to turn off the background photogrammetry

  24. Streamstats https://water.usgs.gov/osw/streamstats/

  25. Other Sources NRCS pdf – determining watershed http://www.epa.gov/owow/watershed/ http://www.dec.ny.gov/lands/25563.html

  26. Next Lecture • Precipitation • Definition • What affects it? • Return period • Probability of an event occurring over a time interval • Design Frequencies • IDF Curves

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